The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Among the materials used in aeronautics, the composite materials represent an increasingly important part. The composite material parts of an aircraft are subjected to stresses, in particular thermal stresses, which may lead to the premature aging of the concerned parts.
These stresses concern in particular the propulsion units, namely the turbojet engines and the nacelles surrounding the turbojet engines. Indeed, the members of the turbojet engines and nacelles made of composite materials are subjected to significant thermal variations. For example, in the case of a nacelle, these members are at ambient temperature on the ground, and undergo in flight either very low temperatures (for the members located in the area called cold area of the nacelle), or very high temperatures (for the members located in the area called hot area of the nacelle).
The composite material parts of the nacelles are qualified depending on minimum mechanical characteristics for an exposure at a first given temperature over the service life of the aircraft, and at a second given temperature (a peak temperature, greater than the first temperature) over a short exposure duration accumulated during the lifespan of the aircraft.
In practice, it happens that the composite materials are subjected to temperatures greater than or equal to the second threshold, for a duration causing an unacceptable decrease of the mechanical properties.
It is consequently desirable to be capable of characterizing in an accurate and rapid manner the thermal aging of a composite material member, in particular in order to evaluate the level of loss of the mechanical characteristics of this member.
Methods which allow characterizing thermal aging by evaluating the degree of discoloration of a paint called basecoat are known. However, these are of relative accuracy because the quality of the evaluation is highly dependent on the application of the basecoat (variations in thickness, surface condition, etc.). Furthermore, these methods are naturally applicable only to painted parts, which represent a noteworthy disadvantage in view of the presence of numerous unpainted parts made of composite material.
Moreover semi-destructive control methods are known. These methods require the taking of a material sample whose mechanical characteristics are then analyzed, for example methods of the dynamic mechanical analysis type (also known as DMA, for “Dynamic mechanical analysis”). However, this type of method requires taking a large-sized sample, whose subsequent repair does not fall within the scope of the repairs called “cosmetic repairs”.